1. Field
This invention relates to constant current detector systems and constant current generators. In particular, this invention provides for a system having bypassable detectors which detect an external stimulus by causing a predictable voltage change at the output of a constant current generator. More specifically, it provides a system to detect personnel cable transport system malfunctions and stop the personnel cable transport system upon the occurrence of a malfunction.
2. State of the Art
Known detector systems typically employ voltage sources and rely on electrical circuit parameter variances (e.g. current) in detecting circuitry. These systems are limited to environments in which the ambient temperature is relatively constant absent the use of costly components and/or more components to adapt them to a wide range temperature environment.
For example, the ambient temperature environment for a safety detector system used with a personnel cable transport system (e.g., ski chair lift, aerial tram, gondola, and the like) typically found at ski recreation areas may vary from well below 0.degree. Fahrenheit to temperatures well above freezing (e.g., 40.degree. to 60.degree. Fahrenheit). Indeed, some personnel cable transport systems are even operated in the summer when ambient temperatures frequently exceed 80.degree. Fahrenheit. Detector systems heretofore known are not readily or economically adaptable to such an environment or are not fully capable to monitor all desirable safety aspects. Accordingly, a detector system which is workable for all safety aspects in a wide temperature range environment is desirable.
Other known systems which may be regarded as comprised of a string of (detector) switches are not necessarily affected by ambient temperature. However, such systems are undesirable because they are very difficult to troubleshoot in the event of a failure. Further, such systems are very susceptible to lightening damage. That is, stray voltages may be generated by the lightening in the wiring between towers. Those voltages can damage the system detector switches because they may be of sufficient magnitude to weld or vaporize switch contacts.
Yet other known systems of the type which are comprised of a string of switches (in series) may have a resistor associated with each (detector) switch which is electrically included in a bridge circuit or its equivalent when its (detector) switch detects (operates). Balance networks may then be used to locate the operating switch. However, such systems are typically incapable of handling two or more malfunctions.
It may also be noted that detector systems heretofore known employ detectors or detecting circuitry in cooperation with a centralized unit to receive and process detection signals. The failure of any one or more of such detectors may, in some cases, render the entire system inoperative. In other cases, the detector may generate a detection signal because of an intermittent environmental condition. In such circumstances, it may be desirable to bypass the concerned detector. Further, it may also be desirable to keep track of which detectors are bypassed.
In some cases, detectors may be located at some substantial distance from each other and from a centralized unit to receive and process detection signals. To properly test and align and to effectively maintain such a system, communication between a technician at the centralized unit and at one or more detectors may be required. Systems heretofore known do not provide for such communication.